Ballastable concrete bases for offshore platforms are known which are constituted by solid concrete walls. These bases may be suitable for use in cold seas since they are strong enough to resist the pressure of ice, which may be very high, but they suffer from the drawback of being very heavy. Attempts have been made to lighten them by using lightweight concrete, but this solution is expensive and not entirely satisfactory.
Preferred embodiments of the present invention provide a base which may be made from normal concrete, which has high strength, and which is nevertheless of reasonable weight.